Closteroviruses

Closteroviruses are a group of plant viruses in the family Closteroviridae. They are distinguished by unusually long, filamentous, flexuous virions and very large RNA genomes. Virions can be several micrometers in length and are among the longest known plant virus particles. The genome is positive-sense single-stranded RNA.

Genome organization varies among the genera, but most closterovirids have a large 5' replicase gene and additional downstream modules encoding movement proteins and coat proteins. The replication strategy typically involves expression of the replicase as a polyprotein with regulatory frameshifts, and subgenomic RNAs for downstream genes. Genome size is among the largest for plant RNA viruses, and segmentation occurs in the Crinivirus genus, whereas Closterovirus and Ampelovirus members usually have a single genomic RNA.

The family Closteroviridae contains three genera: Closterovirus, Ampelovirus, and Crinivirus. Notable members include Citrus tristeza virus (CTV) and Beet yellows virus (BYV) in Closterovirus; Grapevine leafroll-associated viruses (GLRaV) in Ampelovirus; and several Criniviruses such as Lettuce infectious yellows virus, which have bipartite genomes and are typically whitefly-transmitted.

Hosts are predominantly plants, including many crops and ornamentals. Transmission vectors are diverse and genus-specific, with aphids commonly transmitting Closterovirus and CTV, mealybugs and soft scale insects transmitting Ampeloviruses, and whiteflies transmitting Criniviruses.

Diagnosis relies on serology and molecular methods (such as RT-PCR). Management emphasizes vector control, use of virus-free planting material, crop sanitation, and regulatory measures to prevent movement of infected material.